Photographic process and product



United States Patent 3,433,635 PHOTO-GRAPHIC PROCESS AND PRODUCT Howard G. Rogers, Weston, Mass., assignor to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware No Drawing. 'Continuation-in-part of application Ser. No. 112,509, May 25, 1961. This application Jan. 25, 1966, Ser. No. 522,815 US. Cl. 96-29 13 Claims Int. Cl. G03c 5/54, 1/64 ABSTRACT OF THE DISCLOSURE Photographic processes and products for forming color images wherein a ferric salt is employed as the lightsensitive material, color image formation being predicted upon one of the following two systems: (1) reduction of a reducible color-providing material, e.g., an azo dye, by ferrous ions formed as a function of exposure; or (2) oxidation of an oxidizable silver halide developing agent by ferric ions remaining after exposure.

This application is a continuation-in-part of application Ser. No. 112,509, filed May 25, 1961 and now abandoned.

This application relates to photography or more particularly to products, processes and compositions useful in obtaining color images.

It is known that ferric salts are light sensitive, forming ferrous ions where exposed to light. The present invention makes use of the light-sensitive properties of ferric salts to provide novel means for obtaining color images.

It is therefore one object of this invention to provide novel means for obtaining color images.

Another object of this invention is to provide novel means for obtaining either positive or negative color images, as the practitioner may so desire, by diffusiontransfer processes.

A still further object is to obtain color images or reproductions of an original by utilization of the lightsensitive properties of ferric salts.

Yet another object is to provide novel systems for obtaining color images, utilizing either the ability of ferrous ions to reduce a color-providing material or ferric ions to oxidize a color-providing material, image formation being in terms of unreacted color-providing material.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

As was indicated previously, the present invention makes use of the light-sensitive properties of ferric salts. It has been suggested that the ferrous ions formed as a result of exposure of a ferric salt to light will reduce silver salts to form a visible silver image. For example, US. Patent No. 2,886,435 discloses a process wherein a support containing a layer of ferric salt is first exposed to light and then contacted with a silver salt. Where exposed,

ferrous ions are formed and these ions according to the teachings of the patent act as reducing agents to develop the silver salts. After rinsing, fixing and washing, the silver image thus obtained may be treated in any of the known ways whereby color images may be obtained, namely by bleaching and color development, oxidation and reduction process, toning, dye toning, ozobromone, dye imbibition, and the like.

It has also been suggested that the light-sensitive ferric salts be utilized in photographic processes along with a coupler which diiferentiates between the ferric salt and the ferrous salt formed as a result of exposure, to form a visibly distinguishable reduction product with one or the other. Processes of this nature are described, for example, in Us. Patent No. 2,846,309, issued to Edwin H. Land.

It has further been suggested that ferric salts such as ferric chloride may be employed to oxidize hydroquinones to quinones. In US. Patent No. 2,357,944, use has been made of this property to isolate Vitamin K principles. As far as known, however, no practical photographic use has heretofore been made of the oxidizing properties of ferric salts.

In addition to the teachings of the aforementioned patents, there is also described, in US. Patent No. 2,543,- 181, issued to Edwin H. Land, diffusion transfer processes whereby ferric salts of organic acids are exposed and then developed with suitable reagents capable of differentiating between ferric and ferrous salts to form a visible image.

The present invention makes use of ferric salts to form either positive or negative color images in a manner neither suggested by any of the above-mentioned prior patents nor suggested by any other prior disclosures or practices known to the photographic art.

It has now been found that color images or reproductions of originals can be obtained by using a 'ferric salt or salts as the light-sensitive material in photographic products and processes such as are described in more detail below. The ferric salts useful in the practice of this invention may be any of the light-sensitive ferric salts heretofore known in the art. As examples of light-sensitive ferric salts, mention may be made of ferric salts of inorganic acids, such as ferric chloride, and ferric salts of organic acids, such as fern'c tartrate, ferric oxalate, and ferric citrate.

As was mentioned previously, when a light-sensitive ferric salt is exposed, an imagewise distribution of ferrous ions is formed in terms of exposed areas. According to the present invention, use may be made of this imagewise distribution of ferrous ions in exposed areas to reduce a reducible color-providing material, or, alternatively, use may be made of the ferric ions in unexposed areas to oxidize an oxidizable color-providing material, color image formation in either instance being in terms of unreacted color-providing material, i.e., unreduced or unoxidized color-providing material, as the case may be, as distinguished from prior art processes wherein image formation is in terms of a colored reaction product, e.g., a coupling reaction to form a colored product.

According to one embodiment of the invention, color images may be obtained by processes utilizing the reducing properties of ferrous ions. In this embodiment, a lightsensitive element containing a layer of suitable light-sensitive ferric salt is exposed to light, say, for example,

through a transparency, to form ferrous ions in areas of exposure or of partial exposure. The thus-exposed lightsensitive layer is then brought into intimate contact with a reducible color-providing material by and in the presence of an aqueous alkaline processing solution. The ferrous ions formed as a result of exposure then selectively reduce the reducible color-providing material, thereby effecting a color change and/ or a change in chemical or physical properties of the color-providing material in exposed areas.

By reducible color-providing material is meant any reducible material which by itself or by subsequent treatment such as, for example, by coupling, is capable of providing a color at least in the reduced state.

As examples of reducible color-providing materials contemplated by this invention, mention may be made of dyes which undergo a color change or a loss of color upon reduction. Included within this category are dyes which are bleached by reduction. Illustrative of these so-called bleachable dyes which are useful in the practice of this invention are azo dyes which are soluble in the processing solution. Such azo dyes are well known in the art. As examples of useful azo dyes, mention may be made of azo dye developers, that is, azo dyes that are also silver halide developing agents, such as are disclosed in U.S. Patent No. 2,983,606. In addition to the aforementioned Patent No. 2,983,606 and further illustrative of useful azo dye developers, mention may be made of the monoand diazo dye developers disclosed in U.S. Patents Nos. 3,134,672, 3,222,169, 3,230,086, 3,142,565, and 3,186,982 as well as those disclosed in the following applications which were copending with the aforementioned parent application, Ser. No. 112,509; 612,054 (abandoned in favor of 197,283, filed May 24, 1962); 612,055 (abandoned in favor of 192,355, filed May 4, 1962); 680,403, filed Aug. 26, 1957 (now abandoned); 703,515 filed Dec. 18, 1957 (now abandoned); 707,109, filed Ian. 6, 1958 (now abandoned); and 748,145, filed July 14, 1958 (now abandoned). It is also contemplated that oxidized dye developers, such as the quinone oxidation product of the aforementioned azo dye developers, may be employed as the bleachable dyes.

While the preferred class of the reducible dyes which undergo a color change upon reduction are azo dyes, it will be appreciated that the invention is not so limited. Obviously other dyes known in the art which undergo a color change upon reduction may be employed in the practice of this invention.

When the reducible color-providing material is a dye which undergoes a color change upon reduction, such as an azo dye as described above, the dye may initially be present in a light-sensitive element comprising the dye, a layer of the light-sensitive ferric salt and preferably also a suitable support such as and, for example, a subcoated cellulose acetate sheet or other such supports well known in the art. Where the dye is initially present in the lightsensitive element, it may, for example, be situated in a separate layer adjacent to the layer of ferric salt. In other words, the layer of dye may be located between the support and the layer of ferric salt. It is contemplated that where found desirable or expedient to do so, the layer of dye and layer of ferric salt may be separated by a suitable spacer layer such as, for example, a gelatin spacer. Spacers of this nature are likewise well known in the art. It is further contemplated that the dye may be located in the same layer as the ferric salt. If a dye developer is utilized as the color-providing material in the same layer as the ferric salt, the dye developer should preferably be encapsulated for reasons which will be disclosed in more detail below in the discussion of another embodiment of the invention. Encapsulation of the dye may be effected by any of the means known in the art such as, for example, according to the disclosures of U.S. Patent No. 2,800,- 457 and U.S. Reissue Patent No. 24,899.

In either event, a positive image may be obtained by exposing the light-sensitive element and then contacting it with an aqueous alkaline processing solution whereby the ferrous ions formed as an incident of exposure are brought into an intimate contact with the dye, thereby effecting the desired color change in terms of areas of exposure.

It is also contemplated that the dye may initially be present in the aqueous alkaline processing solution, in which case a layer of ferric salt is exposed and then contacted with an equeous alkaline processing solution containing the dye, to form a positive image in the manner described above.

In any of the processes described above, excellent colortransfer images may also be obtained by utilization of diffusion-transfer techniques such as described in the aforementioned U.S. Patent No. 2,543,181, wherein the light-sensitive element is exposed and then imbibed with the aqueous alkaline processing solution, which is also a solvent for the dye, thereby transferring at least some of the dye to a superposed image-receiving layer to form a positive image thereon. Since both the reduced and the unreduced dye are soluble in the processing solution, it is possible to remove substantially all of the dye from the light-sensitive element, thus forming a positive transfer image of relatively great density. It is also possible to transfer only a portion of the dye, thereby forming positive images of lesser but still significant and useful density on both the light-sensitive element and the image-receiving layer.

The aqueous alkaline processing solution may be applied by immersing, coating, spraying, fiowing, etc., but the application is accomplished preferably, at least where a transfer image is sought, by rupture of a frangible container and spreading of the processing solution contained therein, according to the teachings of the aforementioned U.S. Patent No. 2,543,181 or U.S. Patent No. 2,634,886, both issued to Edwin H. Land.

A viscosity-increasing compound which, when spread over a water-absorbent base will form a relatively firm, dimensionally stable film, may be included in the liquid processing solution to assist in carrying out uniform spreading of the solution between the layer of the exposed salt and the image-receiving layer. A suitable film-forming material is a high molecular weight polymer such as, for example, a polymeric water-soluble ether; such as hydroxyethyl cellulose or sodium carboxymethyl cellulose. Film-forming compositions of this nature are described in U.S. Patent No. 2,559,643. It is also contemplated that the processing'solution may contain other additives of known function such as organic solvents, ingredients to regulate the pH of the solution, and the like.

Another class of reducible color-providing materials which may be utilized in the practice of this embodiment of the invention may be defined as reducible immobile color-providing substances.

By the expression immobile color-providing sub stance, as used herein, is meant a color-providing substance or a derivative thereof which in its initial condition is not appreciably diffusible in the liquid processing composition, at least during the period of imbibition. The immobile color-providing substance contains a functional group which is reductible by the ferrous ions formed by exposure of the ferric salt to provide a color-providing substance which is difiusible in the liquid processing composition.

It should therefore be appreciated that whereas the formation of color images from color-providing materials which undergo a color change upon reduction is dependent upon the selective reduction and hence change in color in the exposed areas, the formation of color images by the use of immobile color-providing substances is dependent upon the differential insolubility and thus differential n0ndiffusibility caused by the initially immobile color-providing substance being rendered soluble and thus diffusible by reduction in areas of exposure. It should also be apparent that whereas positive transfer images are obtained when using the former class of color-providing substances, negative transfer images are obtained in the latter case. When employing reducible color-providing materials which are immobile or relatively immobile in their original state but which are rendered mobile upon reduction by ferrous ions, one may also obtain a positive image in terms of unreacted, i.e., unreduced, color-providing material by removal of the reduced and mobile color-providing material, e.g., by washing, image formation thus being in terms of the immobile material remaining in unexposed areas of the light-sensitive element.

In addition to the above-mentioned types of colorproviding substances which are in the general nature of complete dyes, it is also contemplated to employ incomplete dyes such as color couplers which contain a reducible group. As examples of such materials, mention may be made of couplers which are immbilized or otherwise rendered incapable of coupling upon reduction, image formation thus being obtained in terms of unreacted coupler.

A photosensitive element was prepared by coating a subcoated cellulose acetate film base with a tetrahydrofuran solution containing 2% cellulose acetate hydrogen phthalate and 3% of 2-[p-2',5-dihydroxyphenethyl)phenylazo]-4-n-propoxy-1-naphthol of the formula:

I OH

After this layer had dried, a coating was applied of a gelatin solution containing 2% ferric chloride and 2% tartaric acid. The resulting photosensitive element was then exposed to a sunlamp for 5 minutes and processed by applying an aqueous solution containing 3% sodium hydroxide and 4% sodium carboxymethyl cellulose in a thin layer between the photosensitive element and a superposed image-receiving layer prepared by coating a cellulose acetate-subcoated baryta paper with a solution containing 4% N-methoxymethyl polyhexamethylene adipamide in 80% aqueous isopropanol. After an imbibition period of approximately 2 minutes, the image-receiving element was separated from the photosensitive element to reveal a positive magenta image on both the receiving element and the photosensitive element. Since most of the dye was transferred to the receiving element, the transfer image was of greater density and contrast than that in the photosensitive element.

In the foregoing embodiment of the invention, the formulation of the color image was effected by utilization of the reducing properties of ferrous ions.

In another embodiment of the invention, the formation of the color image is effected by the oxidative properties of ferric ions. It has been found that ferric ions will oxidize a silver halide developing agent wherein the developing function contains at least one hydroxy group such as, for example, orthoand para-dihydroxybenzene, orthoand para-aminophenol, 1,4- and 1,2-dihydroxynaphthalene, and 2- and 4-aminonaphthalene, or substituted derivatives thereof.

It should therefore be appreciated that the reaction mechanism whereby the image is formed in this embodiment of the invention is dependent upon the oxidation of the developing agent in unexposed areas by the ferric ions, oxidation being precluded in exposed areas due to the conversion of ferric ions to ferrous ions. Thus, in its broadest form, this embodiment of the invention embraces the concept of selectively oxidizing a silver halide developing agent in unexposed areas to form an imagewise distribution of oxidized developing agent in terms of unexposed areas and unoxidized developing agent in terms of exposed areas, and utilizing the differential between the oxidized and unoxidized developing agents to form a color image. This differential may be a change in color, a change in physical properties, such as a differential in solubility in a given processing solution, or a change in chemical properties, such as a difierential ability to couple or to react with another component at some time subsequent to exposure to form the color image.

In a preferred form of this embodiment of the invention, use is made of dye developers, that is, developing agents having the above-mentioned characteristics and which are also dyes.

As in the embodiment previously described, the dye developer may initially be present in the light-sensitive element along with the ferric salt or it may be dissolved in the processing solution. If the dye developer is situated initially in the light-sensitive element, it is advisable to maintain it in spaced relationship from the ferric salt, as by the aforementoned spacer layer or by encapsulation of the dye developer, in order to prevent oxidation of the dye developer prior to exposure.

The light-sensitive element is exposed in the manner previously described and then imbibed with an aqueous, non-alkaline and preferably substantially neutral, processing solution, containing an organic solvent for the unoxidized dye developer, thereby effecting intimate contact between the ferric salt and the dye developer.

In unexposed areas, the ferric ions oxidize the dye developer, thereby rendering it insoluble in the aqueous processing solution. Transfer of unoxidized dye developer to a superposed image-receiving layer therefore occurs only in terms of exposed areas, thereby forming a negative transfer image in or on the image-receiving layer and leaving a positive image in the light-sensitive element.

Since image formation is dependent upon oxidation of the developing function and not upon the character of the dye moiety of the compound, any dye developers containing the designated developing function, such as the dye developers disclosed in the aforementioned US. Patent No. 2,983,606, may be employed in the practice of this embodiment. Thus, for example, they may be azo dye developers such as disclosed in the aforementioned patents and copending US. applications. They may also be dye developers formed from other than azo dyes, such as the dye developers disclosed in US. Patents Nos. 2,983,605; 3,076,808; 3,076,820; 3,126,280; 3,135,506; 3,135,606; etc., as well as those disclosed in the following applications which were copending with the parent application, Ser. No. 112,509; 485,840, filed Feb. 3, 1955; 849,727, filed Oct. 30, 1959 (now abandoned); 1,443, filed Jan. 11, 1960, etc.

While in the preferred embodiment the developing agent is a dye developer, that is, a developing agent which is also a complete dye, it is within the scope of the invention to utilize developing agents which are not complete dyes, but are capable of providing color image-forming constituents in one of the oxidized and reduced states.

Thus, for example, it is within the scope of the invention to utilize ordinary silver halide developing agents Which are oxidizable by ferric ions such as, for example, hydroquinone or its derivatives. Such developing agents may be used, for example, in combination with couplers which will react with the oxidized developing agent to form a relatively insoluble dye. In reaction mechanisms of this nature, the ferric salt is exposed and then imbibed with an aqueous processing solution, as in the foregoing illustrations of the invention, to bring the exposed ferric salt into intimate contact with the developing agent, whereby the ferric ions oxidize the developing agents. The oxidized developing agent is then contacted with the coupling component to form a positive dye image on the light-sensitive element, thus permitting transfer by imbibition only of unoxidized and therefore unreacted developing agent and coupler to a superposed image-receiving layer. Oxidation of the unreacted developing agent to cause the desired coupling in or on the image-receiving layer may be effected by aerial oxidation or by incorporation into the image-receiving layer of conventional oxidizing agents such as sodium perborate; sodium perchlorate; ammonium dichromate, etc. Processes involving the oxidation of developing agents and subsequent coupling to form color images, and particular developing agents and couplers useful in such processes, are disclosed with particularity in US. Patents Nos. 2,559,643; 2,661,293; and 2,698,798, all issued to Edwin H. Land.

It is also within the scope of the invention to utilize the reaction mechanism involving complete dyes which react with oxidized developing agents to form products or substances of less mobility or dependent color characteristics. Dyes of this nature and processes involving their reaction with oxidized developing agents are described with more particularity in US. Patent No. 2,774,668, issued to Howard G. Rogers.

It is also within the scope of the invention to use silver halide developing agents such as leuco' 1,4-dihydroxyanthraquinone, 1,4,5,8-tetrahydroxy-anthraquinone, etc., which in their oxidized state possess a color. Developing agents of this nature distinguish from dye developers, since the former class of compounds depend upon an oxidation reaction to produce a color. Where developing agents of this nature are employed, the oxidized developing agent is immobile or rendered less soluble in the processing solution and the unoxidized developing agent is then transferred to an image-receiving layer and subsequently oxidized in the manner described above to produce a negative transfer image. Examples of such developing agents are described in US. Patent No. 2,892,710.

The following example shows by way of illustration and not by way of limitation the embodiment of this invention wherein developing agents are oxidized and the differential between the oxidized and unoxidized developing agent is utilized to form the color image.

Example 2 A photosensitive element prepared in the manner described in Example 1 was exposed to a sunlamp for minutes and processed by applying an aqueous solution containing 2% carboxymethyl cellulose, 20% acetone, and 10% ethyl Cellosolve, in a thin layer between the eX- posed photosensitive element and a superposed imagereceiving element prepared in the manner described in Example 1. After an imbibition period of about 2 minutes, the image-receiving element was separated from the photosensitive element and contained a negative image of good contrast and density.

It should be noted that in the embodiment described in Example 2, no spacer layer was used. Thus while it may be found desirable in some instances to maintain the ferric salt and the dye developer in spaced relationship prior to exposure, as was stated previously, it is not necessary to the practice of this invention to do so.

Since certain changes may be made in the above products and processes without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

'1. A photographic product comprising a support, a photosensitive element including a layer on said support comprising a light-sensitive ferric salt which will form ferrous ions upon exposure to light, an azo dye reducible by ferrous ions in a layer on the same side of said support as said ferric salt; and an image-receiving layer adaptable for being placed in super-position with said layer of dye and for having imparted thereto a dye transfer image.

2. A photographic product comprising a photosensitive element including a support, a layer on said support comprising a light-sensitive ferric salt which will form ferrous ions upon exposure to light, and a silver halide developing agent oxidizable by ferric ions in a layer on the same side of said support as said ferric salt and an image-receiving layer adaptable for being placed in superposition with said layer of developing agent and for having imparted thereto a dye transfer image.

3. A photographic product comprising a support, a layer on said support comprising a light-sensitive ferric salt which will form ferrous ions upon exposure to light, and a dye developer oxidizable by ferric ions in a layer on the same side of said support as said ferric salt.

4. A product as defined in claim 3 wherein said dye developer is an azo dye developer.

5. A process for forming images in color which comprises exposing a layer containing a light-sensitive ferric salt to form ferrous ions in terms of areas of exposure; contacting said exposed layer with a solution containing a material selected from the group consisting of image dyes and intermediates for said dyes reducible by ferrous ions formed as a function of exposure and silver halide developing agents oxidizable by ferric ions remaining in unexposed areas of said layer, reacting said material with one of said ferrous ions formed in areas of exposure and said ferric ions remaining in unexposed areas; forming an imagewise distribution of unreacted material; transferring said imagewise distribution of unreacted material, at least in part, to a superposed stratum; and forming on said stratum a color image in terms of said unreacted material.

6. A process as defined in claim 5 wherein said material comprises a complete dye.

7. A process as defined in claim 6 wherein said dye is an azo dye.

8. A process as defined in claim 6 wherein said dye is a dye developer.

9. A process of forming images in color which comprises exposing a photosensitive element containing a light-sensitive ferric salt to form an imagewise distribution of ferrous ions in terms of exposed areas and an imagewise distribution of ferric ions in terms of unexposed areas; contacting said exposed photosensitive element with an alkaline solution containing an azo dye which is reducible by ferrous ions to form an imagewise distribution of reduced dye in terms of areas of exposure and an imagewise distribution of unreduced dye in unexposed areas, and transferring by imbibition at least part of said imagewise distribution of unreduced dye to a superposed stratum to form thereon a positive color image in terms of said unreduced dye.

10. A process of forming images in color which comprises exposing a photosensitive element containing a light-sensitive ferric salt to form an imagewise distribution of ferrous ions in terms of exposed areas and an imagewise distribution of ferric ions in terms of unexposed areas; contacting said exposed photosensitive element with a solution containing a color-providing material selected from the group consisting of dyes and dye intermediates whose mobility in said solution is differentially affected by one of said ferric and ferrous ions, said material being oxidizable by ferric ions or reducible by ferrous ions to provide said differential in mobility, thereby providing an imagewise distribution of more mobile colorproviding material; transferring at least part of said imagewise distribution of said more mobile material, by

imbibition, to a superposed stratum; and forming on said stratum a color image in terms of said more mobile material.

11. A process of forming images in color which comprises exposing a photosensitive element containing a light-sensitive ferric salt to form an image'wise distribution of ferrous ions in terms of areas of exposure and an imagewise distribution of ferric ions in terms of unexposed areas; contacting said exposed element with a nonalkaline solution containing a p-dihydroxyphenyl silver 10 halide developing agent oxidizable by ferric ions to form an imagewise distribution of oxidized developing agent in terms of unexposed areas and an imagewise distribution of unoxidized developing agent in terms of exposed areas, said unoxidized developing agent being more soluble in said solution than said oxidized developing agent; transferring by imbibition at least part of said imagewise distribution of unoxidized developing agent to a superposed stratum; and forming a negative color image thereon in terms of said unoxidized developing agent.

12. A process as defined in claim 11 wherein said de' veloping agent is a dye developer.

13. A process as defined in claim-12 wherein said dye developer is an azo dye developer.

References Cited UNITED STATES PATENTS 2,559,643 7/1951 Land 96-29 2,837,987 6/1958 Land 9629 FOREIGN PATENTS 597,982 2/ 1948 Great Britain. 670,883 4/ 1952 Great Britain.

15 NORMAN G. TORCHIN, Primary Examiner.

A. T. SURO-PICO, Assz'szant Examiner.

US. Cl. X.R. 

